Laboratory Analysis
First-line peripheral blood laboratory evaluation should include complete blood count with differential, complete metabolic panel including total protein, albumin, and liver functions, lactate dehydrogenase (LDH), lipid panel, and, in the case of chylous ascites, lipase. Depending on the severity of lymphatic leak, secondary laboratory evaluations may include PT/ aPTT/ INR and fibrinogen to monitor for the ongoing development of coagulopathy and an immunoglobulin panel (IgA, IgG, IgM) to monitor for the ongoing development of hypogammaglobulinemia.
Aspiration of fluid via thoracentesis or paracentesis is critical to establish a diagnosis of lymphatic leak. Simple observation of the aspirated fluid can start to differentiate the fluid as exudative (e.g. lymphatic) versus transudative (from heart failure, hepatic cirrhosis, nephrotic syndrome) in origin.[16] If the child has been enterally fed, chyle will appear cloudy, milky white although it can also appear serous, sanguineous or bloody. Evaluation of the pleural or peritoneal fluid that supports lymphatic origin include elevated concentration of protein, LDH, triglyceride, increased presence of lymphocytes, and the presence of chylomicrons (Table 2) . If three is concern for PLE, stool can be evaluated for alpha-1-antitrypson.
Biopsies of abnormal lymphatic tissue may help with histologic diagnosis of disease, but caution should be taken in the setting of lymphatic leak not to risk exacerbating the condition. Biopsy of involved rib bones can be particularly dangerous as this may exacerbate lymphatic leak. In conjunction with clinical history, physical examination, imaging and fluid analysis, if biopsy is felt to be helpful, biopsy of affected tissue remote from an active leak is recommended.